<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        div{
            width: 800px;
            height: 400px;
            background-color: pink;
            display: flex;
            justify-content: center;
            /*侧轴默认对齐方式*/
            /*align-items: flex-start;*/
            /*我们需要一个侧轴居中对齐*/
            /*align-items: center;*/
            /*align-items: flex-end;*/
            /*拉伸，但是子盒子不要给高度*/
            align-items: stretch;
        }
        div span{
            margin: 10px;
            width: 150px;
            /*height: 100px;*/
            background-color: skyblue;
        }
    </style>
</head>
<body>
<div>
    <span>1</span>
    <span>2</span>
    <span>3</span>
</div>
</body>
</html>
